1. Field of the Invention
The present invention relates to a process for manufacturing an electrical contact pin having a fixing part to be fitted into a through hole of a circuit board without using any solder.
2. Description of the Prior Art
Electrical contact pins of this type are sometimes called "press fit contactors" and disclosed for example in U.S. Pat. Nos. 4,223,970 issued to Leo Walter on Sept. 23, 1980, and 4,464,009 to Hartmuth Thaler on Aug. 7, 1984, and Japanese Patent Kokai No. 58-123,678.
Walter Patent discloses a compliant backplane electrical connector having a pin with four edges at the corners of the generally rectangular, Z-shaped cross section of the pin. Such edges penetrate the plating of an opening upon insertion of the pin into the opening.
Thaler Patent discloses a solderless connector pin for electrical circuits. It has an elongated deformable region having an M-shaped or W-shaped cross section. Upon insertion of the pin into a bore, the deformable region deforms elastically and, in the case of a small diameter bore, partially plastically to provide a good electrical and mechanical connection between the pin and the plate.
Japanese Pat. No. 58-123,678 discloses, as shown in FIG. 6(D), a contact pin consisting of a fixing part 1 having an N-shaped cross section with a pair of triangular recesses 2 and 3 arranged in an alternating fashion on opposite sides. In order that corners 4 and 5 adjacent to these triangular recesses fully abut the conductive through hole of a circuit board, the opposite corners of the terminal are rounded to form chamfers 6 and 7. The fixing part 1 of contact pin 9 with such structure has a springy accordion-like property.
The following is one of the methods of manufacturing such contact pins by using a press machine. This process may be illustrated as follows:
(1) As FIG. 6(A) shows, upper and lower metal dies 20 and 30 have triangular projections 21 and 31 to form the triangular recesses 2 and 3 and rounded corners 22 and 32 to form chamfers 6 and 7, respectively, of a metallic work or fixing part 1.
(2) These dies are mounted on a press and pressed against the metallic work 1 in the vertical direction. As FIG. 6(B) shows, indefinite burrs or fins 2' and 3' are formed because of the presence of triangular projections 21 and 31 and rounded corners 22 and 32.
(3) As FIG. 6(C) shows, these undesired burrs or fins 2' and 3' are cut off by a pair of press cutters 22 and 33.
(4) As FIG. 6(D) shows, finally, a fixing part having an N-shaped cross section is completed.
Electrical contact pins having such a springy accordion-like fixing part as described above have been developed so as to fit into through holes in a certain range of diameters of a circuit board. However, they still have the following disadvantages:
(1) Where the diameter of a through hole is relatively large, although the corners 4 and 5 adjacent to the triangular recesses can abut the conductive wall of a through hole making electrical connection, the other corners or chamfers 6 and 7 cannot abut the conductive wall, thus as a whole making poor connection and increasing contact resistance especially after a vibration or shock has been applied for a long period.
(2) Where the diameter of a through hole is relatively small, the non-springy chamfers 6 and 7 strongly abut the conductive wall (solder layer) and badly damage it, thus increasing contact resistance or making conduction impossible because of complete separation of the conductive wall from the through hole.
(3) The indefinite burrs or fins 2' and 3' formed in the pressing step are so small that it is a difficult operation to cut them off. In addition, the resulting cuts become broken surfaces 6b and 7b as shown in FIG. 6(D) making the corners 4 and 5 imperfect or too short to cut into the conductive wall of a through hole or reducing the accordion-like spring force of the corners.